The invention relates to a rotary piston machine comprising a chamber formed in a housing in which three-blade rotors rotate in opposite directions around parallel spaced axes and intermesh so as to be free of contact forming separate cells with the peripheral wall of the chamber and with each other.
Rotary piston machines with three-blade rotors are known as Roots blowers. In such machines, the inlet and the outlet are arranged in alignment with each other along a line that is perpendicular to the axes of the rotors. The volume flow is conveyed by the intermeshing blades in the chamber and pushed out of the outlet without internal compression. Such a rotary piston machine is especially suited as a loader for relatively high volume flows.
The invention provides a rotary piston machine with three-blade rotors that works with internal compression and internal expansion and that is suitable for generating pressure as well as vacuum, even in the case of relatively small volume flows.
With the rotary piston machine according to the invention, the claw-like blades of the rotors, together with the chamber, simultaneously define a suction cell whose volume increases during the rotation of the rotors and they also define a pressure cell whose volume decreases when the rotors rotate. Since the rotary piston machine works with internal compression and, at the same time, with internal expansion, it is suitable for simultaneously generating pressure and negative pressure.
In a further embodiment of the invention, the rotors, together with the chamber, define two charging cells that are initially separated from each other during the rotation of the rotors and that, during the further rotation of the rotors, are united with each other to define the pressure cell. A medium can be fed in via the charging cells so that, at the pressure outlet, an accordingly enlarged volume flow is available. Before being united, the charging cells are shifted essentially isobarically and isochorically in the pump chamber; the medium present in the charging cells does not undergo any considerable change in pressure or volume during the shift of the charging cells.
The geometry of the rotors is determined by the requirement that, in the chamber, the cells necessary for simultaneously generating pressure and vacuum have to be separated from each other. Since the rotors interact so as to be free of contact with each other as well as with the peripheral wall of the chamber, no wear occurs in the area of the pump chamber. The sealing gap between the rotors can be kept very small by optimizing their geometry; in practical embodiments, this gap is just fractions of a millimeter, so that good pressure and vacuum values are ensured. These values even improve with increasing service life since the deposits that form over time reduce the size of the sealing gaps.
The rotary piston machine according to the invention is especially well suited for use as a pump for simultaneously generating compressed air and vacuum. In this application, it is particularly well suited for use in the paper-processing industry, especially in cases that do not require a separate supply or adjustment of compressed air and vacuum. Compressed air is needed, for example, to blow air onto a stack of paper from the side to help separate the sheets. The generation of pulsating compressed air by such a pump proves to be very practical here since the paper edges can be separated more easily by means of the pulsating compressed air that is generated. At the same time, negative pressure is required in such applications to pick up the top sheet of paper.